Stop the local (Physical) machine from being able to use the USB device. This will mean that vWorkspace is always able to redirect it.
1. On the Physical machine, Open Device Manager from the Control Panel.
2. Find the USB device in the list of devices.
3. Select the Properties of your USB devicel from Device Manager
4. Select the Details tab from the USB Properties sheet.
5. Use the dropdown list to select the Hardware Ids option
6. Right click and copy the top value from this list*
With this USB ID you can create and configure a GPO.
7. Click the Start button, select Run, then type gpedit.msc, then click the OK button.
8. Expand Computer Configuration|Administrative Templates|System|Device Installation|Device Installation Restrictions
9.Double-click on the Prevent installation of devices that match any of these hardware IDs policy.
10. Select the Enabled radio button.
11. Click on the Show button to open the Show Contents dialog box.
12. Paste in the ID for the USB Device that you copied in step 6
13. Tick the "Also apply to matching devices that are already installed"
14. Save all of your settings from within the policy and exit the editor.
* Step 6 may have several values. Usually, the top value is all that is required. You may need to copy additional values into the GPO.